U.S. patent application number 16/084490 was filed with the patent office on 2019-03-14 for semiconductor laser device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Rei HASHIMOTO, Tsutomu KAKUNO, Kei KANEKO, Shinji SAITO, Osamu YAMANE.
Application Number | 20190081456 16/084490 |
Document ID | / |
Family ID | 59851381 |
Filed Date | 2019-03-14 |
![](/patent/app/20190081456/US20190081456A1-20190314-D00000.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00001.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00002.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00003.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00004.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00005.png)
![](/patent/app/20190081456/US20190081456A1-20190314-D00006.png)
United States Patent
Application |
20190081456 |
Kind Code |
A1 |
YAMANE; Osamu ; et
al. |
March 14, 2019 |
SEMICONDUCTOR LASER DEVICE
Abstract
A semiconductor laser device includes an active layer, a first
layer, and a surface metal film. Multiple quantum well layers are
stacked in the active layer; and the active layer is configured to
emit laser light of a terahertz wave by an intersubband transition.
The first layer is provided on the active layer and includes a
first surface in which multiple pits are provided to form a
two-dimensional lattice. The surface metal film is provided on the
first layer and includes multiple openings. Each of the pits is
asymmetric with respect to a line parallel to a side of the
lattice. The laser light passes through the multiple openings and
is emitted in a direction substantially perpendicular to the active
layer.
Inventors: |
YAMANE; Osamu; (Yokohama,
JP) ; SAITO; Shinji; (Yokohama, JP) ; KAKUNO;
Tsutomu; (Fujisawa, JP) ; KANEKO; Kei;
(Yokohama, JP) ; HASHIMOTO; Rei; (Edogawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
|
Family ID: |
59851381 |
Appl. No.: |
16/084490 |
Filed: |
September 2, 2016 |
PCT Filed: |
September 2, 2016 |
PCT NO: |
PCT/JP2016/075859 |
371 Date: |
September 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/105 20130101;
H01S 5/3402 20130101; H01S 5/2228 20130101; H01S 5/12 20130101;
H01S 5/2027 20130101; H01S 5/04254 20190801; H01S 5/14 20130101;
H01S 5/18 20130101 |
International
Class: |
H01S 5/12 20060101
H01S005/12; H01S 5/18 20060101 H01S005/18; H01S 5/34 20060101
H01S005/34; H01S 5/042 20060101 H01S005/042 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2016 |
JP |
2016-051671 |
Claims
1: A semiconductor laser device, comprising: an active layer
configured to emit laser light of a terahertz wave by an
intersubband transition, a plurality of quantum well layers being
stacked in the active layer; a first layer having a first surface
and being provided on the active layer, a plurality of pits being
provided in the first surface to form a two-dimensional lattice;
and a surface metal film provided on the first layer, a plurality
of openings being provided in the surface metal film, each of the
pits being asymmetric with respect to a line parallel to a side of
the lattice, and the laser light passing through the plurality of
openings and being emitted in a direction substantially
perpendicular to the active layer.
2: The semiconductor laser device according to claim 1, wherein the
lattice of the first layer includes the pits having configurations
of prescribed regions of the first layer cut out from the first
surface toward a depth direction.
3: The semiconductor laser device according to claim 1, wherein the
openings form a two-dimensional lattice.
4: The semiconductor laser device according to claim 2, wherein the
openings form a two-dimensional lattice.
5: The semiconductor laser device according to claim 3, wherein a
pitch of the lattice of the openings is different from a pitch of
the lattice of the first layer.
6: The semiconductor laser device according to claim 4, wherein a
pitch of the lattice of the openings is different from a pitch of
the lattice of the first layer.
7: The semiconductor laser device according to claim 1, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
8: The semiconductor laser device according to claim 7, wherein the
first electrode includes a frame portion and a plurality of stripe
portions, two end portions of each stripe portion being linked to
the frame portion, and the plurality of stripe portions obliquely
crosses the frame portion and is arranged to be mutually parallel
at a prescribed pitch.
9: The semiconductor laser device according to claim 8, wherein an
opening of the first electrode is asymmetric with respect to a line
parallel to a side of the lattice of the first layer.
10: The semiconductor laser device according to claim 2, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
11: The semiconductor laser device according to claim 3, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
12: The semiconductor laser device according to claim 4, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
13: The semiconductor laser device according to claim 5, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
14: The semiconductor laser device according to claim 6, further
comprising a first electrode provided between the first layer and
the surface metal film, electrically connected to a surface of the
first layer, but insulated from the surface metal film.
Description
TECHNICAL FIELD
[0001] This invention relates to a semiconductor laser device.
BACKGROUND ART
[0002] When using a quantum cascade laser as a light source of a
terahertz wave, a laser oscillation of 30 GHz to 30 THz is possible
due to an intersubband transition of electrons.
[0003] In the case where an edge emitting quantum cascade laser is
used as the light source, a collimator lens is necessary to cause
the spreading laser light emitted from the end surface to be
parallel light; and the exterior form of the laser device becomes
large.
PRIOR ART DOCUMENT
Patent Document
[0004] [Patent Document 1] JP 2009-231773 (Kokai)
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0005] A semiconductor laser device is provided that is capable of
emitting a terahertz wave of a plane wave with high efficiency.
Means for Solving the Problem
[0006] A semiconductor laser device of an embodiment includes an
active layer, a first layer, and a surface metal film. Multiple
quantum well layers are stacked in the active layer; and the active
layer is configured to emit laser light of a terahertz wave by an
intersubband transition. The first layer is provided on the active
layer and has a first surface in which multiple pits are provided
to form a two-dimensional lattice. The surface metal film is
provided on the first layer and has multiple openings. Each of the
pits is asymmetric with respect to a line parallel to a side of the
lattice. The laser light passes through the multiple openings and
is emitted in a direction substantially perpendicular to the active
layer.
BRIEF DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a schematic perspective view of a semiconductor
laser device according to a first embodiment.
[0008] FIG. 2 is a schematic plan view of the surface metal film of
the semiconductor laser device according to the first
embodiment.
[0009] FIG. 3 is a graph illustrating the transmittance for the
frequency of the terahertz wave of the surface metal film of the
semiconductor laser device according to the first embodiment.
[0010] FIG. 4 is a schematic plan view illustrating a modification
of the surface metal film.
[0011] FIG. 5 is a schematic plan view illustrating another example
of the arrangement of the openings of the surface metal film.
[0012] FIG. 6 is a schematic plan view of the surface emitting
portion of the semiconductor laser device of the first
embodiment.
[0013] FIG. 7 is a schematic plan view of the first electrode of
the surface emitting portion.
[0014] FIG. 8 is a partial schematic perspective view of the pit
portion.
[0015] FIG. 9 is a graph illustrating the current injection
uniformity dependence and the relative light extraction efficiency
dependence with respect to the number of pits.
[0016] FIG. 10 is a schematic perspective view of a semiconductor
laser device according to a second embodiment.
[0017] FIG. 11 is a configuration diagram of a laser device
according to a comparative example.
EMBODIMENT OF INVENTION
[0018] Embodiments of the invention will now be described with
reference to the drawings.
[0019] FIG. 1 is a schematic perspective view of a semiconductor
laser device according to a first embodiment.
[0020] The semiconductor laser device 5 includes an active layer
25, a first layer 27, and a surface metal film 80. Multiple quantum
well layers are stacked in the active layer 25; and the active
layer 25 is configured to emit laser light of a terahertz wave by
an intersubband transition. In the specification, the terahertz
wave is taken to be not less than 30 GHz and not more than 30
THz.
[0021] The first layer 27 is provided on the active layer 25 and
has a first surface 21a in which multiple pits 101 are provided to
form a two-dimensional lattice. The surface metal film 80 is
provided on the first layer 27; and multiple openings 80a are
provided in the surface metal film 80. The openings 80a can be, for
example, the gaps of a metal mesh, etc.
[0022] The planar configuration of each of the pits 101 is
asymmetric with respect to a line parallel to a side of the
lattice. Also, laser light 60 passes through the multiple openings
80a and is emitted in a direction substantially perpendicular to
the front surface of the active layer 25. The light intensity of
laser light 61 emitted by passing through the openings 80a of the
surface metal film 80 is measured by a detector 90 such as a
bolometer, etc. In the specification, the substantially
perpendicular direction is not less than 81 degrees and not more
than 99 degrees with respect to the front surface of the active
layer 25.
[0023] In the embodiment, the semiconductor laser device 5 further
includes a first electrode 50 provided between the first layer 27
and the surface metal film 80, electrically connected to the
surface of the first layer 27, but insulated from the surface metal
film 80. Although the surface metal film 80 is illustrated as being
separated from the surfaces of the first layer 27 and the first
electrode 50 in FIG. 1, actually, the surface metal film 80 is
stacked with an insulating body or the like interposed.
[0024] A stacked body 21 includes the first layer 27, the active
layer 25, and a second layer. The multiple pits 101 that have
opening ends at the first surface 21a of the stacked body 21 are
provided in a two-dimensional lattice configuration and act as a
periodic-structure PC (photonic crystal). For example, the pits 101
have configurations in which triangular pyramid regions are cut out
from the first surface 21a of the stacked body 21 toward the depth
direction.
[0025] The laser light 60 can have optical resonance along a QCL
optical resonance direction 300 inside the active layer 25; and the
mode is selected by the periodic-structure PC and further emitted
from the first surface 21a along an optical axis substantially
perpendicular to the first surface 21a due to a diffraction effect.
In other words, the region lower than the first electrode 50
functions as a surface emitting portion. A voltage is supplied
above and below the stacked body 21.
[0026] FIG. 2 is a schematic plan view of the surface metal film of
the semiconductor laser device according to the first
embodiment.
[0027] In the drawing, one opening 80a of the surface metal film 80
is provided for four pits 101. The laser light 60 is emitted from
the surface emitting portion in an upward direction substantially
perpendicular to the front surface of the active layer 25, passes
through the openings 80a, and is emitted to the outside. The laser
light 60 is a TM (Transverse Magnetic) wave polarized in the
direction of the arrow.
[0028] For the square lattice that forms the periodic-structure PC,
the crossing point of two orthogonal sides D and E in the XY plane
is taken as a lattice point G; and the lattice spacing of the
square lattice is taken as M. For example, the lattice point G can
be considered to be the centroid of the planar configuration of the
pit 101, etc. Each of the pits 101 has non-line symmetry with
respect to one side of the two sides D or E of the square lattice.
The lattice may not be a square lattice and may be a lattice in
which two sides are orthogonal.
[0029] A portion of the terahertz wave can pass through the opening
80a. For example, by changing the configuration and/or the size of
the opening 80a, the transmittance of a tera hertz wave of a
wavelength of the width of the opening 80a or more can be set to
50% or more. Also, the surface metal film 80 in which the openings
80a are provided acts as an external (LC) resonator for the
terahertz wave. In the case where a fine particle 90 including a
dielectric adheres at the opening 80a vicinity of the surface metal
film 80, the resonant frequency of the external resonator changes.
Therefore, the peak frequency of the transmission spectrum shifts.
In other words, the first embodiment can emit a plane wave
terahertz wave with high efficiency by using a metamaterial as the
surface metal film 80.
[0030] Also, in the semiconductor laser device 5 of the first
embodiment, the transmission peak frequency can be shifted because
the surface metal film 80 is used as an external resonator. The
detection of fine particles, etc., can be performed by detecting
the shift of the transmission peak frequency. For example, it is
taken that the fine particle 90 including a microbe, bacteria such
as coliform bacteria, or the like is adhered at the opening 80a
vicinity of the surface metal film 80 of the opening 80a.
[0031] In the case where the wavelength of the laser light is near
visible light, the change of the transmittance due to the fine
particles 90 is reduced by the amount of a region corresponding to
the cross-sectional area of the fine particles 90 and is therefore
small. Conversely, in the case where the wavelength of the laser
light is near a terahertz wave, the shift amount of the resonant
frequency is large even if the amount of the fine particles 90 is
low; therefore, the change of the transmittance is in a wide
frequency range. Therefore, the existence or absence of the fine
particles 90 can be detected with high accuracy. The fine particles
90 include PM 2.5, etc.
[0032] FIG. 3 is a graph illustrating the transmittance for the
frequency of the terahertz wave of the surface metal film of the
semiconductor laser device according to the first embodiment.
[0033] The vertical axis is the transmittance (%); and the
horizontal axis is the frequency (THz) of the terahertz wave. After
immobilizing coliform bacteria, water was dropped; and the
transmission spectrum was measured. The initial state is
illustrated by the broken line; the state after the coliform
bacteria immobilization is illustrated by the dotted line; and the
state after the dropping of the water is illustrated by the solid
line. The transmission spectrum intensity is measurable using a
spectrometer, etc.
[0034] By immobilizing the coliform bacteria, the peak frequency
decreased about 25 GHz with respect to the initial state. By
dropping the water, the peak frequency decreased about 300 GHz (the
transmittance was about 33%). The absorption coefficient of water
for the terahertz wave is high and is about 10.sup.6 times the
absorption coefficient for visible light or the like. Therefore,
the shift amount of the resonant frequency after dropping the water
onto the immobilized fine particle 90 becomes large; and the
detection accuracy of the fine particle 90 increases.
[0035] In the case of only water not including the fine particle
90, the shift amount of the resonant frequency is larger than the
shift amount when the fine particle 90 exists. For example, a
single wavelength of the laser light 60 can be set within a range
including the peak vicinity of the initial spectrum and the peak
vicinity of the fine particle spectrum after dropping the
water.
[0036] FIG. 4 is a schematic plan view illustrating a modification
of the surface metal film.
[0037] In the modification of FIG. 4, the planar configuration of
the opening 80a is a cross shape. In the case where the fine
particle 90 is placed directly on the surface metal film 80, the
chip of the semiconductor laser device 5 should be replaced after
the measurement. If the fine particle 90 is placed on a plate that
is transparent to the terahertz wave, it is unnecessary to replace
the chip.
[0038] FIG. 5 is a schematic plan view illustrating another example
of the arrangement of the openings of the surface metal film.
[0039] The pitch of the openings may be equal to the pitch M of the
two-dimensional diffraction grating. Or, it is unnecessary for the
pitch of the openings to be an integer multiple of the pitch M of
the two-dimensional diffraction grating. In other words, it is
sufficient for the openings 80a to be arranged so that the resonant
frequency is shifted.
[0040] FIG. 6 is a schematic plan view of the surface emitting
portion of the semiconductor laser device of the first
embodiment.
[0041] The pit 101 has a configuration in which a triangular
pyramid, a truncated triangular pyramid, or the like is cut out
downward from the first surface 21a of the stacked body 21. The
configuration of the pit 101 is not limited thereto. In the
drawing, the opening end of the pit 101 is illustrated by a right
triangle. The two sides that sandwich the right angle are parallel
respectively to the two sides of frame portions 50a and 50b; and
the oblique side is parallel to a stripe portion 50c of the first
electrode 50.
[0042] The active layer 25 has a configuration in which a
relaxation region is stacked alternately with an intersubband
transition light emitting region made of a quantum well layer
including a well layer and a barrier layer. The quantum well
includes, for example, a well layer made of
In.sub.0.669Ga.sub.0.331As doped with Si, and a barrier layer made
of In.sub.0.362Al.sub.0.638As doped with Si. It is more favorable
for the quantum well layer to have a multi-quantum well (MQW:
Multi-Quantum Well) structure in which at least two well layers and
multiple barrier layers are further stacked alternately. Also, the
relaxation region also can include a quantum well layer.
[0043] A QCL has TM (Transverse Magnetic) polarized light of which
the polarization direction is parallel to the front surface of the
active layer 25; and for resonator mirrors sandwiching the active
layer from the front surface and the back surface as in a p-n
junction surface emitting laser, stimulated emission does not occur
because the propagation directions of the light and the polarized
light are aligned. In other words, it was impossible to realize a
VCSEL (Veryical Cavity Surface Emitting Laser: surface emitting
laser).
[0044] Conversely, in the QCL according to the first embodiment, it
is possible to resonate and amplify the stimulated emission light
because the propagation direction of the stimulated emission light
is a direction parallel to the front surface of the active layer
25. Further, in the case of a structure that is periodic and has
anisotropy in the periodic structure, it is possible to extract the
stimulated emission light in a direction substantially
perpendicular to the front surface of the active layer 25. That is,
a surface emitting laser is realizable in which the wavelength
region is longer than the mid-infrared region which was previously
realizable only by a QCL.
[0045] In the surface emitting laser, it is unnecessary to form a
resonator by cleaving as in an edge emitting laser; and the
decrease of the yield due to the cleaving can be prevented.
Further, in an edge emitting laser, the resonator is first formed
by the cleaving; therefore, it is necessary to perform inspections
after cleaving; and the cost of inspection is high compared to an
LED or the like for which the inspections can be performed using an
auto-prober or the like for the wafer as-is.
[0046] Conversely, the QCL according to the first embodiment can be
evaluated by an auto-prober in the wafer state; a large effect of
reducing the inspection cost and/or the cost from the perspective
of yield can be expected; and mass production and price reduction
are easy for QCLs which had previously been expensive.
[0047] FIG. 7 is a schematic plan view of the first electrode of
the surface emitting portion.
[0048] For the stripe portion 50c, the width is taken as L1; and
the pitch in a direction orthogonal to the stripe portion 50c is
taken as L2. The multiple pits 101 are disposed in the region
sandwiched between the stripe portions 50c.
[0049] FIG. 8 is a partial schematic perspective view of the pit
portion.
[0050] The stacked body 21 can further include a contact layer 28
on the first layer 27. Also, an insulator layer 40 of SiO.sub.2,
etc., can be provided on the first surface 21a. The surface metal
film 80 can be planarized by further providing an insulator layer
of SiO.sub.2, etc., inside the pits.
[0051] FIG. 9 is a graph illustrating the current injection
uniformity dependence and the relative light extraction efficiency
dependence with respect to the number of pits.
[0052] The horizontal axis is the number of pits inside one period
of the stripe portion 50c of the electrode; and the vertical axis
is the uniformity of the current injection and the relative light
extraction efficiency. In the case where the stripe portion 50c of
the first electrode 50 has a one-dimensional periodic structure,
the uniformity of the current injection is normalized to be 100 in
the case where two pits are included inside one period along a
direction orthogonal to the stripe portion 50c.
[0053] Also, in the case where the stripe portion 50c of the first
electrode 50 has a one-dimensional periodic structure, the relative
light extraction efficiency is normalized to be 100 in the case
where fifty pits are included inside one period along the direction
orthogonal to the stripe portion 50c.
[0054] As the number of the pits 101 inside one period along the
direction orthogonal to the stripe portion 50c increases, the
uniformity of the current injection decreases; but the relative
light extraction efficiency increases. In other words, by setting
the number of the pits 101 inside one period to be not less than 5
and not more than 20, both the uniformity of the current injection
and the laser light extraction efficiency can be realized. Thus,
the optimal solution is determined from the relationship between
the surface area of an opening 50d of the first electrode 50 and
the efficiency of the current injection and the relationship of the
effect of the periodic structure of the first electrode 50 on the
diffraction effect of the light extraction.
[0055] FIG. 10 is a schematic perspective view of a semiconductor
laser device according to a second embodiment.
[0056] The first electrode is not provided in the semiconductor
laser device according to the second embodiment. In other words,
the surface metal film 80 functions as the first electrode and
supplies a voltage to the surface emitting portion. The first
electrode is unnecessary in the second embodiment; therefore, the
manufacturing processes can be simple; and a cost reduction is
easy. The low cost is favorable in the case where the chip of the
semiconductor laser device 5 is replaced. The surface metal film 80
and the surface of the surface emitting portion (the surface of the
first layer 27) actually are closely adhered despite being
illustrated as being separated in FIG. 10.
[0057] FIG. 11 is a configuration diagram of a laser device
according to a comparative example.
[0058] A semiconductor laser element 105 that is used as a light
source is an edge emitting QCL emitting single-mode laser light.
The edge emitting QCL emits the laser light from the ridge
waveguide in a direction orthogonal to the end surface of the ridge
waveguide. In such a case, the beam diverges; and the cross section
of the beam has an elliptical configuration. Therefore, the
diverging emitted light is caused to be parallel light by using a
collimating lens 200, etc.
[0059] The parallel light that is irradiated from the light source
105 is reflected by a reflection plate 180, subsequently is
concentrated by a lens 202, and is incident on a detector 190 such
as a bolometer, etc.; and the light intensity of the parallel light
is detected. The reflection plate 180 can be a metal plate having
openings. For a terahertz wave, such an optical configuration is
large such that the planar configuration of the laser device is
several tens of cm.times.several tens of cm or the like; and the
adjustment of such an optical configuration is not easy.
[0060] Conversely, according to the semiconductor laser device of
the embodiment, the terahertz wave is emitted from the surface
emitting portion substantially perpendicular upward from the active
layer 25. Therefore, a complex configuration and a large optical
system are unnecessary; therefore, a small semiconductor laser
device that can emit a plane terahertz wave with high efficiency is
possible.
[0061] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
invention.
* * * * *